The present disclosure relates generally to electrodes, and more particularly to electrodes having macropores and micropores therein.
Fuel cells use an electrochemical energy conversion of fuel (including but not limited to hydrogen, propane, methane, carbon monoxide, and the like) and oxidant(s) into electricity and heat. It is anticipated that fuel cells may be able to replace primary and secondary batteries as a portable power supply. In fuel cells, the fuel (usually containing a source of hydrogen) is oxidized to produce (primarily) water and carbon dioxide. Liberated electrons from the oxidation and reduction reactions occurring at the electrodes, result in a useful electrical potential difference and current through the load.
Many fuel cells make use of alternative fuels, such as hydrocarbons or alcohols, which are converted into hydrogen via a chemical process. Electrochemical fuel cells employing alcohols (e.g. ethanol, methanol, etc.) as a fuel are referred to as Direct Alcohol Fuel Cells (DAFC) and more specifically, those employing methanol are referred to as Direct Methanol Fuel Cells (DMFC). In a DMFC, the methanol molecule's carbon-hydrogen and oxygen-hydrogen bonds are broken to generate electrons and protons at the site of the anode. One potential problem with DMFC is that methanol may diffuse or “crossover” from the anode to the cathode via diffusion. If the fuel reaches the cathode, it may adsorb onto the cathode catalyst and react with oxygen, resulting in a parasitic loss of fuel and poisoning the alcohol-intolerant cathode catalyst, thereby decreasing the performance.
Attempts for reducing methanol crossover include: structural modifications of the electrolyte membrane; reduction in the delivered concentration of the fuel; and the addition of a metal hydride barrier layer. Modifying the electrolyte membrane may be difficult due to the relatively high methanol permeability of such membranes. A reduction in the delivered concentration of the fuel may result in reduced catalytic efficiency. Potential problems associated with the metal hydride barrier layer may include cracking and delamination, which may occur as a result of hydration cycling. In addition, the metallic layer may have poor adhesion to a traditional polymer electrolyte membrane, due, at least in part, to the expansion and lack of mechanical integrity of both the metallic layer and solid electrolyte.
As such, it would be desirable to provide an electrode that substantially prevents fuel crossover in a fuel cell while substantially maintaining its efficiency.